strings extraction: extract values with custom UTF encoding from strings

[zekker6]

Previously, only quoted values of UTF escaped sequences were converted into UTF runes due to Go strings semantics. Also, it would not decode values with non-standard Go escaping.

This change adds additional decoding logic to always convert escape sequence into character.

See also: VictoriaMetrics/VictoriaMetrics#5519

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.63%. Comparing base (6ea382c) to head (e6e2f46).

Files with missing lines	Patch %	Lines
lexer.go	85.00%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
+ Coverage   89.05%   89.63%   +0.58%     
==========================================
  Files          11       11              
  Lines        3681     3010     -671     
==========================================
- Hits         3278     2698     -580     
+ Misses        306      212      -94     
- Partials       97      100       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.